1. Field of the Invention
The invention relates to a method and apparatus for determining the foaming characteristics of crude oil streams at the wellhead.
2. Background of the Invention
The foaming characteristics of crude oil streams produced from a well are important in designing apparatus for separating the crude oil stream into oil and gas. The most common method of separating oil and gas produced from a well is to pass the oil and gas mixture under an initial high pressure into a vessel under reduced pressure wherein the gases dissolved in the oil flash off the oil and the heavier oil separates from the gas by gravity. The volume of the vessel and the retention time of the oil is sufficient to allow the oil to accumulate and is withdrawn from the bottom portion of the vessel with the separated gas being withdrawn from the top portion of the vessel. As gas separates from the oil, foam accumulates on the top of the oil and the amount of foam formed will vary depending upon the characteristics of the crude oil being produced. Therefore, the capacity of the vessel must be sufficient to accommodate the volume of foam formed in the vessel based upon the foaming characteristics of the crude oil and crude oil production.
Conventionally, separators are designed on the basis of broad general experience. They commonly are sized to be larger than would be required to handle predicted production through the vessels. As a result, there is no adequate procedure for the design of separator vessels that are optimally sized for the production stream. Nor is there a good procedure for the sizing of separators for a new oil field, based on properties of oil samples taken in drill stem tests of discovery wells. As a result, significant amounts of money are wasted in the costs of offshore platform construction, for both deck space and supportive capability, as well as in the costs of oversized vessels.
Presently, the foaming characteristics of oil are measured by bubbling a gas through a sparger tip into a given volume of oil, contained in some suitable measuring vessel. This practice is unsatisfactory because the character of the sparger tip may change over a period of usage and resulting foams are not be properly comparable. Furthermore, the bubbles of foam formed with sparger systems are usually larger than those which result from the self-nucleation of foam by decreasing the pressure on a gas-saturated liquid, i.e., when the gas is "flashed" from the liquid.
In copending application to C. L. Humphries et al filed June 18, 1982, Ser. No. 390,098, now U.S. Pat. No. 4,426,879 there is disclosed a method for measuring the foaming characteristics of crude oil comprising saturating the crude oil with a gas inert to the crude oil under high pressure and passing the gas-saturated oil into a flash separator comprising a transparent elongated horizontal cylinder under reduced pressure wherein the amount of foam formed is measured with respect to the amount of gas withdrawn from the separator and the amount of oil contained therein.
The present invention is an improved method and apparatus for determining the foaming characteristics of crude oil at the wellhead comprising introducing the crude oil stream into a separator under reduced pressure and measuring the amount of foam formed based upon the amount of gas evolved and the amount of oil contained therein.